1. Field of the Invention
The invention relates to a microprocessor, in particular for use in a chip card, with a control unit and with a housing surrounding the control unit. Furthermore, the invention relates to a chip card with such a microprocessor.
To an increasing degree, payment processes for relatively small amounts of money are processed with the aid of a chip card system. In this respect, a chip card has the function of a "money storage facility". There being provided on a chip card a microprocessor which has a control unit, a data memory for storing the amount of money stored on the chip card, interfaces, in particular for inputting and outputting data which are relevant to payments, a control device for controlling the processing procedure of the data which are processed in conjunction with the chip card, and an instruction memory which stores the operating program for the control device. Such chip card systems are used in the field of credit cards, in pay TV application systems and also in systems for monitoring access to devices concerned with security and to buildings.
Shortly after the introduction of the first chip card systems, attempts were made to manipulate chip cards in order to obtain illegitimate advantages with such manipulated chip cards. For example, attempts have been made to simulate chip cards and to provide their data memories with a manipulated credit balance.
This has been counteracted by encrypting the data present in the data memory of the chip card in such a way that it is no longer possible to simulate the data. For this purpose, algorithms such as DES (Data Encryption Standard), PES (Proposed Encryption Standard), DSA (Digital Signature Algorithm), DEA (Data Encryption Algorithm), and RSA (Reversed Shamir-Adelman Cryptoalgorithm) are used.
However, a significant weakness of known chip card systems continues to be that the microprocessor, which is surrounded by a housing, can easily be exposed. To do this, the housing of the microprocessor is subjected to an aggressive substance, such as an acid for example, over a specific period of time, so that the housing is etched away and the microprocessor is exposed. The structural configuration of the exposed microprocessor can then be analyzed. In order to do this, different input signals can be applied to the terminals of the microprocessor, so that information on the program, present in the instruction memory, for controlling the processing procedure can be acquired. This information can be used to decrypt, for example, the data in the data memory.
Published, European Patent Application EP 0 565 480 A2 discloses how to use indicator elements in chip cards which react in an unambiguous and discernible fashion to physical influences or other influences aimed at destroying the function of chip the cards.
Published, Non-Prosecuted German Patent Application DE 41 15 398 A1 discloses a method for manufacturing a biosensor with a planarized surface which reduces the risk of diaphragms tearing. It includes the steps of producing a gate insulator, producing and structuring a polysilicon layer, implementing a source and a drain, exposing an active gate region, arranging an ISFET within a housing in such a way that the active gate region of the ISFET comes to be situated within a window of the housing, and applying the biological or biochemical diaphragm to the active gate region.
The paper "An ISFET-FIA System for High Precision pH Recording" in Sensors and Actuators B, 15-16 (1993) 68-74 (P. Woias et al.) discloses an ISFET sensor for measuring a pH value in a fluid which has a high degree of stability and high measuring accuracy even at low flow velocities.
Published, European Patent Application EP 0 481 881 A1, corresponding to U.S. Pat. No. 5,465,349, discloses an integrated circuit which has a program memory, a data memory, an I/O port and a register. The register stores the signals of the sensors for unusual operating conditions. When unusual operating conditions occur, the microprocessor stops operating.